shader.c: Fix bad free

We were freeing the file instead of freeing the buffer, oops.

shader.c

@@ -21,8 +21,8 @@ static const char *load_txt(const char *name)
 	s = malloc(len+1);
 	if(fread(s, 1, len, f) != len)
 	{
-		free(f);
 		fclose(f);
+		free(s);
 		return NULL;
 	}